The invention relates to a process and device for the gasification of fine-grain fuel materials, such as powdered fuel materials from coal, petroleum coke, biological waste or fuel materials as well as liquid fuels originating from oil, tar, refinery residues and other liquid residues suited for being atomised in the gasifier in order to generate raw synthesis gas mainly consisting of carbon monoxide and hydrogen and hereinafter named raw gas.
A large number of processes and devices of this type are known already. Typical constructions are those with slag discharge at the bottom and gas outlet at the top. U.S. Pat. No. 3,963,457 describes a Koppers-Totzek gasifier with horizontal burners facing each other, a slag discharge at the bottom, gas outlet and gas quench at the top and a process with recycled, cooled gas. EP 0 400 740 B1 describes a Shell gasifier with a horizontal burner, slag discharge at the bottom and gas outlet at the top and upward gas quench and with a vertical mixing pipe. U.S. Pat. No. 4,936,871 describes a Koppers gasifier with a gas outlet at the top and upward gas quench and likewise provided with a vertical mixing pipe. U.S. Pat. No. 5,441,547 outlines a PRENFLO gasifier also provided with a gas outlet at the top and upward gas quench and likewise equipped with a vertical mixing pipe, a reversing device and downward heat exchanger. U.S. Pat. No. 4,950,308 deals with a Krupp-Koppers gasifier with a horizontal burner, slag discharge at the bottom and gas outlet at the top as well as radiation cooler and gas quench. Most of the Koppers-Totzek gasifiers had a water quench that permitted cooling down to approx. 1000° C. which was far from the dew point of the generated gas, nozzles being used for water spraying.
The disadvantage of these technologies was the elevated construction of the unit and a lack of adequacy for further downcooling of the generated raw gas. In case it would have been intended to use a water quench unit with surplus water permitting cooling of the synthesis gas down to the dew point, there would have been a risk that water penetrated into the burners arranged at the level below; which constituted a safety risk. Moreover, thermo-dynamic demerits would have occurred if the quench water had penetrated into the reaction zone of the gasifier.
There are also specific types of gasifier construction that have holes in the bottom for the discharge of the raw gas and slag as well as a water quench with immersion pipe. U.S. Pat. No. 4,247,302, for example, describes a Texaco gasifier with a burner arranged in the upper part and with a common discharge opening for gas and slag at the bottom. A separation vessel is fitted below the gasifier from which the slag flows downwards into the slag bath whereas the synthesis gas is piped through a lateral outlet and into a gas quench vessel. The disadvantage of this type is the fact that several vessels are required and that the system tends to clogging because hot slag particles that are not yet solidified must be conveyed, which particularly applies to the pipeline between the separation vessel and the quench vessel.
U.S. Pat. No. 4,494,963 deals with a Texaco gasifier with burner arranged in the upper part and a common outlet for gas and slag in the lower part. A liquid quench unit arranged below the said gasifier mainly consists of a pipe wetted with a coolant, such as water, and submerged in the water bath. Patent EP 0 278 063 A2 describes a similar system. Patent EP 0 374 324 A1 specifies how to wetten the inside of such an immersion pipe. Further typical types of construction are outlined in documents U.S. Pat. No. 4,992,081 and U.S. Pat. No. 5,744,067.
The deployment of an immersion pipe wetted with a liquid film prevents the formation of incrustations. The said film covers the wall, performs a vertical motion, cools and thus prevents the formation of incrustations. A demerit of the concept, however, is that the quench outlet temperature depends on the size and dwelling time of the gas bubbles in the water bath, which in turn influence several factors, such as the gas throughput, pressure, solids content in the water bath; this causes variation of the outlet temperature and precludes an efficient separation of the flue ashes. In addition, the lower end of the immersion pipe alternately comes into contact with very hot gas and with water, so that rapid material fatigue and formation of incrustations will occur.
Types of construction that are also known provide for a downward stream of the generated synthesis gas and slug and for a spray-type quench unit for cooling. Patent DE 40 01 739 A1, for example, describes such a gasifier, underneath which water is sprayed upon the hot gas at various levels in the form of spray cones. The cooled gas leaves the quench zone via a lateral outlet while the slag falls into a water bath. A similar technology is described in WO 98/45388 A2.
Patent DE 10 2005 048 488 A1 specifies a system equipped with several burners arranged symmetrically in the reactor head, the generated raw gas and the slag being jointly treated in a quench cooler using water sprayed for cooling down to the dew point in the range of 180° C. to 240° C., or partial cooling with simultaneous exploitation of the waste heat. Patent DE 10 2005 041 930 A1 describes how to simultaneously withdraw the slag and raw gas at the bottom, condensate water being injected by one or several rows of nozzles arranged in a circle, the slag being discharged via a water bath. The dust is removed at the end of the quench zone. Patent DE 10 2005 041 931 A1 further describes a partial quench system using nozzles arranged in the shell and cooling down to approx. 700-1100° C. with the aid of condensate water; a waste heat boiler is arranged downstream of the said unit.
Document DE 197 51 889 C1 describes a gasification process in which the hot raw gases leaving the gasifier are cooled with the aid of a quench nozzle. The ashes leave the reactor via an intensely cooled slag chute and are washed and cooled in the quench nozzle. The quench nozzle is equipped with a slag drop-off edge and a thorough mixing is obtained by means of a constriction in the quench nozzle. The slag is subsequently discharged and freed from soot. EP 0 084 343 A1 deals with a coal gasifier operating downwards against a water bath and equipped with a two-stage quench system, the first quench being arranged directly downstream of the gasifier. Document US 2007 006 2117 A1 describes a similar process. Document DE 10 2005 048 488 A1 likewise describes a gasifier which acts against a water bath and provides for quenching with the aid of water spraying.
The disadvantage of this process is that the downward stream of hot gas and the flow of water drops from the nozzles cause an intense circulation in the quench zone so that water drops penetrate the whole quench room. The said water drops, which are in the vicinity of the slag hole, thus cool the slag in such a manner that its surface solidifies and forms stalactites. Fine slag particles and water drops cause incrustations on the walls not wetted by a water film, i.e. dry walls, ceiling, nozzles in particular in the sections which alternately become dry and wet. Whenever water evaporates on the walls, incrustations will form from the impurities. The said stalactites and incrustations consequently lead to major operational problems.
There are also patent documents which describe processes in which the generated synthesis gas and the slag flow downwards separately. DE 197 18 131 A1, for example, specifies a method by which the gasification gas obtained and the melt, specifically a salt melt, are discharged separately. In this case, the synthesis gas is cooled in a discharge device by injecting water or a salt solution via nozzles. The melt is conveyed to its own bath and treated accordingly.